Google's new video chat app has an interesting quirk: You can see a live video feed of who's calling you, even before you pick up the call. Think of it as a digital peephole, before you answer the door.

The search giant unveiled the app, called Duo, on Wednesday at its annual I/O developer conference held at the Googleplex Mountain View, California.

The goal is to make the person on the other end of the call more likely to pick up, said Amit Fulay, a Google product manager who demoed the app in an interview ahead of the event. The act of video calling takes so much coordination -- setting up a date and time -- that Google hopes just seeing a friend on the other end will spur more spontaneous communication. (If you're the one doing the calling, you won't be able to see the other person until they pick up.)

"This could have been my friend who just got engaged and she's showing me the ring," Fulay said after hanging up the demo call.

The app is another example of the tech industry's love affair with chat apps. Facebook, Yahoo, Apple, Microsoft and younger companies like Snapchat all have their offerings, as they flock to get more users on their mobile properties.

This isn't Google's first foray into video calling. The company still has Hangouts, another video chat service, but that app is based on people's email addresses. Duo builds your contact list by scouring your phone directory see who else has the app.

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Duo shows you live video of callers before you pick up

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Other messaging apps, like Facebook Messenger and Snapchat, have text, voice and video calls all baked into one. But Google wanted to keep those things separate with Duo. The idea was to keep it dead simple. There's barely an interface to the app, just your phone's camera screen. With most apps that pile on several different features, those do-it-all apps "are still kind of known for that one thing," said Erik Kay, a Google engineer who worked on Duo.

The app can also switch automatically between a Wi-Fi connection and a cellular connection during a call, depending on which signal is stronger. It's similar to the technology used by Fi, Google's experimental wireless carrier service.

The app is also available for both phones running Google's Android as well as iPhones. So, unlike with Apple's FaceTime, iPhone users will be able to chat with Android users too.